Talk to the colleague first not the manager if you do go down this route. But tbh you don’t know what they’re going through. And it’s also not your business, just do the work.

I had a colleague who would do little for months and didn’t mind it. In fact, because he would mind his own business I liked him more than my other colleagues.

I think you should mind your own business, unless for some reason this is your business, ie if you’re the manager.